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Hypothyroidism Causes in Adults
Common causes of hypothyroidism in adults include:
Autoimmune Thyroiditis (Hashimoto's Thyroiditis)
This inherited condition is the most common cause of hypothyroidism in adults. Hashimoto's thyroiditis is an autoimmune disease in which the body's immune system, or natural defense system, attacks its own thyroid gland. This causes a thyroid enlargement or goiter and progressive thyroid destruction.
Subacute Thyroiditis (inflammation of the thyroid gland after a viral disease or after a pregnancy)
In this condition there is usually a phase of hyperthyroidism (a condition in which the thyroid produces an excess of thyroid hormones) followed by a hypothyroid phase. Eventually thyroid function returns to normal. The three types of subacute thyroiditis are:
Previous Thyroid Therapy
Surgical removal of the thyroid gland may be performed to treat thyroid nodules, hyperthyroidism, or other conditions. Treatment of hyperthyroidism with radioactive iodine also results in destruction of thyroid tissue and may lead to hypothyroidism.
Pituitary and Hypothalamic disease
Both the hypothalamus and pituitary gland are involved in the signaling pathways that control the function of the thyroid gland. Diseases of the hypothalamus and pituitary gland can, therefore, affect the amount of thyroid hormone made and secreted by the thyroid gland. Hypothyroidism due to pituitary disease is termed "secondary hypothyroidism," while hypothyroidism due to hypothalamic disease is termed "tertiary hypothyroidism."
Iodine deficiency does not occur in the U.S.. Only severe iodine deficiency will cause low thyroid hormone levels. This condition may occur in mountainous areas of poor, less industrialized nations. Mild to moderate iodine deficiency is common in many European countries.
Stephanie L Lee, MD, PhD, FACE
Sonia Ananthakrishnan, MD
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